Strand chucks



965 R. P. ZlOLKOWSKl 3,163,904

STRAND CHUCKS Filed June 24, 1965 80 FIG, 6

r y 7/4; 10 M F I G 5 Ronald Bzlz fiififi United States Patent Officemesses Patented Jan. 5, 1965 3,163,904 STRAND CHUCKS Ronald I.Ziollsowsiri, Chicago, Illh, assignor to Supreme Products Corporation,Chicago, Ill. Filed June 24, 1963, Ser. No. 289,924 5 Claims. (Ci.24-426) This invention relates to improvements in strand chucks used forline connectors and as anchor grips, which are designed for repeatedattachment to, and release from wire cable, as employed for example, inprestressed concrete structural members. Certain forms of chucks of thischaracter are shown and described in U.S. Patent No. 3,049,775, grantedAugust 21, 1962 to Elmer I. Ondeck, and assigned to the same assignee asthis application.

Essentially, such chucks comprise a body having a frusto-conical borereceiving a plurality of generally wedge-shaped jaws taperedcomplementarily to the bore, each jaw having an interior face providedwith teeth engaging the cable to implement the friction of the jaws onthe cable. Circumferentially-disposed constricting means are provided tomaintain the jaws in axial alignment for operation as a set. Thus, whenthe cable is' seized by the jaws and the cable and chuck are subjectedto a separating force the jaws are drawn into the bore and, by reason ofthe slidable engagement thereof with the bore in the body, they areforced to close on the cable. The gripping action increases withincrease in tension.

In the case of jaws which have a smooth taper on their exterior, as inthe patent aforementioned, the breaking strength of the cable fails toreach an optimum value during laboratory test. in this connection itwill be understood that the jaw teeth will indent or notch the wirescomprising the cable and that, when the cable is tensioned to thebreaking point during test, it will part at the region of deepestindentation, assuming uniformity in the composition of the cable andteeth of equal form and dimensions. Moreover, the planes of rupture ofthe individual wires appear as so-called shear breaks rather than thedesirable so-called tension breaks. A shear break is evidence that thepressure of the teeth is greater in the region of the break than atanother point along the longitudinal extent of the cable coextensivewith the jaws. Tests have demonstrated that a cable which fails in ashear break separates adjacent the smaller end of the jaws, therebyindicating application of greater pressure in that region than in theremaining length of the jaws. Inasmuch as a tension break is not theresult of shear induced at an excessively indented region along thewires, or at least it is fair to state that in such case theindentations do not contribute materially to a tension break, it isdesirable to avoid the deleterious effects of excessive indenting in alocalized zone.

Accordingly, the principal object of this invention is to provide animproved strand chuck so characterized that the adverse effects oflocalized excessive indentation, as aforesaid, are materially reducedand the breaking strength of the cable greatly enhanced.

Another object is to provide the result just mentioned with minimalalteration in the parts presently recognized as constituting acommercially acceptable device, and at minimum additional cost.

Other objects and advantages will become apparent from the ensuingdescription which, taken with the accompanying drawing, discloses apreferred mode of carrying the principles of the invention intopractice.

In this drawing:

FIG. 1 shows a longitudinal crosssection of a chuck of a well-knowntype, as for example, in accordance with FIG. 3 of the patent mentionedabove, but including the improved jaws of the present invention, andprior to application of its gripping force on the cable;

FIG. 2 shows the chuck of FIG. 1 with the force applied to the cable;

FIG. 3 is a side elevation of the jaw assembly incorporating oneembodiment of the improvement of the present invention;

FIG. 4 is a longitudinal cross-section of an alternative form of theinvention;

FIG. 4a is a longitudinal cross section, similar to that of FIG. 1, butwith the cable omitted, showing a modilied form of the invention;

FIG. 5 illustratesthe shear break in a cable; and

FIG. 6 illustrates the tension break in a cable.

Regarded in its broad aspect, the invention comprises a sleeve having afrusto-conical axial bore therein, together with a plurality ofgenerally wedge-shaped jaws carried within the bore, preferably togetherwith circumferentially-disposed constricting means to maintain the jawsin axial alignment for operation as a set. Considered as a group, thejaws have a common exterior configuration which is substantiallycomplementary to the interior of the bore when the cable is insertedtherebetween but prior to application to the cable of the force forwhich a particular size of chuck has been designed. At this juncture, itwill be recognized that these chucks will vary in dimensions dependingupon the nominal diameter of the cable and the tension to be maintainedtherein by the chuck which is restrained against a fixed abutment.However, commercial chucks are frequently arranged to take more than onesize, e.g., cable of and /2" diameter, the tapered surfaces being sodimensioned as to permit some reasonable range of accommodated diametersof cable. Moreover, it will be understood that the curved exterior faceof the jaws will not necessarily be contiguous to the conical surface ofthe bore throughout the entire range of longitudinal relative positionsof the jaws and sleeve. However, the design is such that, when the chuckis locked up with the cable in final position, the respective arcuatesurfaces of the jaws and bore are essentially in abutment so as toobtain maximum bearing. One type of chuck in common use comprises thesleeve, the set of jaws and means embracing the jaws circumferentiallyto preserve their longitudinal alignment as a set while permitting thejaws to diverge radially; while another type includes a compressionspring and a retaining cap therefor whereby the jaws are urged into thebore as a group. It has been found that when the jaws have a uniformtaper on the exterior, bore-engaging surface, the chuck has been engagedwith the cable and axial force has been applied, that the jaw teethpenetrate the wires of the cable to a greater degree in the region ofthe smaller end of the jaws than at the larger end and that, whenbreaking tension has been applied, rupture will occur in that region asa shear break. As previously mentioned, a shear break indicates thatrupture has been induced largely by localized excessive indentation bythejaw teeth as contrasted with rupture occurring solely by stretchingof the wires, as would be the case where a member is subjected tostretching in a testing machine.

I have found that, by relieving the indenting in the region of thesmaller end of the jaws a substantial increase in breaking strengthresults. Accordingly, the present invention comprises jaws which arerelieved on their outer faces by providing a taper which is steeper thanthe taper of the bore in the body (both tapers being measured as anacute angle to the common longitudinal axis). The steeper taper isdesirably adjacent the smaller end of the jaws for a distanceapproximately /3 to /z of the length of the jaws but may extend farther,even over the whole length of the jaws. Thus, assuming a uniformdiameter of the strand-engaging teeth and teeth of equal form, andapplication of appropriate separating force, i.e. tension, between thecable and the jaws, these latter will be drawn into the bore of the bodyto exert the counte'rbalancing gripping force, that is to say, thethinner wall portion of the jaws, coextensive with the steeper taper,will yield sufliciently in a radial sense to relieve the pressure inthat region and, therefore, the depth to which indentation is present.It will be understood that yielding of the jaws will be greatest at thesmaller end and will gradually diminish as the opposite end of the taperis approached. In an alternative aspect the objects of the invention maybe obtained by relieving the interior wall of the jaws by tapering thegripping face presented by the teeth while keeping the tooth formuniform throughout so that, adjacent the smaller end of the jaws, thecrest of the teeth lie on a frusto-conical reference surface having itslarger base at the smaller end of, the jaws. Such surface extendslongitudinally preferably to /2 of the length of the jaws but may extendthe whole'length. In the case where the interior wall of the jaws isrelieved for only a portion of their length the inner end of thefrusto-conical reference surface will merge into a cylindrical surfaceof uniform diameter, upon which the crest of the remaining teethwilllie.

It will therefore be apparent that, by increasing the angle of taper ofthe exterior of the jaws or, alternatively, locating the teeth on aconical surface, there will be provided a graduated gripping actionon'the cable so that whatever indentation occurs will be substantiallyuni formly distributed over the whole axial extent of the jaws.

Turning now to the drawing, there is shown (FIG. 1) a strand chuck inaccordance with the invention comprising a sleeve having afrusto-conical axial bore 11 flanked on the left end by a shortcylindrical bore 12 to avoid bottoming of the jaws, and on the right endby a threaded bore 13. This latter receives a cap 16 having a threadedboss 17. engageable with the bore 13 and a knurled rim 18, for digitalrotation of the cap into assembled position as seen in FIG, 2. Acompression spring 21 is received in a recess 22 in the cap 16 and isadapted to urge the jaw assembly toward the smaller end of the bore 11.The immediately preceding features are well-known and optional, and aredisclosed in said Patent No. 3,049,775.

The jaw assembly (FIG. 3) comprises a plurality of individual generallywedge-shaped jaws 31, in this case three in. number, curved on theirexterior to be complementary to the bore 11 when the cable is tensionedto the ratedmaximum and the jaws occupy the position shown in FIG. 2. Inorder that the jaws 'will'be retained as a group of jointly movablemembers and retainedin axially aligned relation pending locking-up ofthe chuck resilient means are provided which embrace the jointcircumference. For example, an O-ring 33- of some elastomer encirclesthe jaws and is retained in a groove 34 of semicircular cross-sectioncut into each jaw. In the interest of clarity, the jaws are illustratedas spaced apart in the position they will assume when a cable ofappropriate diameter is received therebetween, it being understood that,in the absence of the cable, the jaws will be in adjacency by reason ofthe resilient member 33. The interior face of each jaw is provided witha plurality of teeth 36, usually of V-form with rounded crest cut as amodified buttress thread into an appropriate blank, whereafter the jawsare formed by slitting the blank longitudinally. Alternatively, theteeth may be annuli. However, the teeth are formed most economically asa helix of uniform diameter in an unslitted blank by means of a tap. Theconfiguration of the teeth as to tooth form and whether helically cut oras individual annuli is well known and, specifically, may be asdisclosed in the mentioned patent.

In accordance with the invention, the arcuate exterior surface of eachjaw or, for that matter, of the jaws regarded as a group is, in theillustrative embodiment, provided with a double taper. At the larger endthe taper x, measured as an angle with the longitudinal axis, is thesame as the taper of the wall surface of the bore 11, and such taperobtains for some portion B of the axiallymeasured length A of the wholetaper. In one commercially successful form the distance A is 1.594" andthe distance B is 0.875" or approximately /2 the whole distance A, andthe distance C is 0.719". However, the proportions may vary dependingupon the characteristics of the material of the chuck and cable but apreferred range for the ratio of B to A may be on the order of from 1:2to 2:3. The remaining length C has some steeper taper y. In thecommercial form just referred to the angle of taper of the bore 11 is 6and the angles x and y are 6 and 7, respectively, measured with respectto the common longitudinal axis.

FIG. 1 shows the several parts of the exemplificative chuck exploded forclarity of illustration and the cable Ztl positioned within the jaws andsubjected only to the slight constrictive force of the resilient member33. In

. FIG. 2 the chuck parts have been assembled and the cable has beentensioned to the desired limit. It will be obvious that separating forceapplied between the chuck and cable has caused the jaws 31 to be forcedinto the bore 11 and the teeth 36 caused to grip the cable. More over,it will be understood that, in accordance with known practice, the chuckis held in a fixed position against a suitable abutment (not shown). Thespring 21 acts continuously to urge the jaws toward the smaller end ofthe bore 11 and, as tension is built up, in the cable, the frictionbetween the same and the teeth fixes the ultimate position of the chuckwith respect to, the stretched cable, all as is well-known in this art.I i

As tension in the cable is increased, the jaws 31 are drawn toward thesmaller end of the bore 11. and compressed into gripping relation with,the cable. Meanwhile, the portion C of each jaw is bent untilthe taperover the distances B and C lie on a common conical surface which is thesame as the taper of the bore 11. The angle x is so selected as to urgethe teeth 36 coextensive with the distance C into gripping engagementwith the cable to some degree of indentation which is graduated from aminimum at the smaller end of the jaws to a maximum at the dividingplane between the distances B and C. Indentation of the teeth over theregion Bis, substantially uniform. Tests have demonstrated that, byminimizing indentation in the region C substantially improved breakingstrength of the cable is achieved. For example, a set of jaws as shownand described in connection with FIG; 3 was assembled as shown in FIG. 1and the cable and chuck subjected to a breaking test. The same series oftests was conducted with. conventional jaws having a uniform taper. Thecable employed was Type 270K of /2" diameter, manufactured by John A.Roeblings Sons Division of TheColorado Fuel and Iron Corporation,Trenton, NewJersey (Bulletin RC. 955). In the case of the conventionaljaws the average breaking, point of twentyone test was 18.1 tons and, inthe case of the jaws according to FIG. 3 the average breaking pointwas,20.3 tons, or an increase of 15% approximately. Furthermore, thebreak in the cable when using conventional jaws was of the shear type(FIG. 5) and, when using the jaws of the invention, the break was of thetension type (FIG. 6). The advantages inherent in the latter result havebeen fully explained above.

Although not confirmed, it appears that the tension in the cablecombined with the bending of the jaws over the distance C modifies thetooth angle and allows the cable, during stretching, to slide on theteeth to produce indentations which are not notches thereby to minimizeparting of the cable.

It is Within the scope of the invention to extend the portion Cthroughout the whole tapered length of the jaws, at an angle, y say of7, and to maintain the taper x of the bore 11 at, say 6 (FIG. 4a). Thus,a graduated gripping effect, i.e., may be obtained over the whole lengthof the teeth 36 with results similar to those heretofore described.

The distance C and the difference in the angles x and y may, as pointedout, vary from one size or range of sizes of chuck to another and inaccordance with the number and size of strands in the cable, the numberand size of the wires composing the strands and their composition andheat treatment, as well as the presence or absence of a core andlubricant. It has been found that the length and angle of the taper C isbest established empirically by testing with chucks employing variouscombinations thereof. Accordingly, where herein I refer to the steepertaper viz. x, as extending over some portion, viz. C, of the jawsbeginning at the smaller end thereof, I intend to imply that such tapermay terminate at any point along the jaws, including the right-hand endthereof. Stated otherwise, the length C and the angle x will be soselected as to be sufficiently good for the purposes of the invention.

In FIG. 4 there is shown an alternative form of the invention whereinthe jaws 31b have a uniform exterior taper corresponding to the taper ofthe bore 11 but in which the teeth 36b are uniform and have their crestslying on a conical surface D at an angle 2. The surface D is subject tothe same considerations as those set forth in connection with thesurface C (FIG. 3). That is to say, the surface D begins at the smallerend of the jaws and extends some, or all of the length of the jaws. Itis to be understood that the teeth of the modified embodiment, regardedindividually, are of conventional form, say V-form buttress, with thecrests positioned on a conical surface which is of gradually diminishingdiameter over the distance D, and that the teeth are not truncated.However the crest may be rounded off slightly, if desired. Thus, as thejaws are actuated into gripping relation with the cable, the teeth willengage the same with a graduated degree of indentation which is less atthe smaller end of the jaws than at the larger end, with a resultingfunction as described in connection with the jaws of FIG. 3.

While I have shown particular embodiments of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

I claim:

l. A strand chuck comprising in combination a body having afrusto-conical bore of some predetermined uniform taper referred as anangle to the longitudinal axis, a plurality of jaws received in andengageable as a set with said bore to grip the strand as the chuck andstrand are subjected to a separating force, each jaw being generallywedge-shaped having an interior surface to grip the strand and anarcuate outer surface having a taper complementary to the bore forsliding engagement therewith, the interior surface of the jawsthroughout the active length thereof being provided with transverseteeth of uniform V-form, the crest of the teeth for a portion of thelength of the jaw adjacent the smaller end thereof being disposed on afrusto-conical surface having its larger diameter at said smaller end,and the crest of the remaining teeth being disposed on a cylindricalsurface forming a continuation of said frusto-conical surface whereby,when the jaws are converged into gripping relation with the strand, theteeth adjacent said larger diameter of the frusto-conical surface imparta lesser gripping action which gradually increases toward the smallerdiameter of said surface.

2. A strand chuck comprising in combination a body having afrusto-conical bore of some predetermined uniform taper referred as anangle to the longitudinal axis, a plurality of jaws received in andengageable as a set with said bore to grip the strand as the chuck andstrand are subjected to a separating force, each jaw being generallywedge-shaped having an interior surface to grip the strand and anarcuate outer surface having a taper complementary to the bore forsliding engagement therewith, the interior surface of the jawsthroughout the active length thereof being provided with transverseteeth of uniform V-form, the crest of the teeth being disposed on afrusto-conical surface having its larger diameter at the smaller end ofthe jaws and its smaller diameter at the larger end of the jaws whereby,when the jaws are converged into gripping relation with the strand, theteeth adjacent said larger diameter of the frusto-conical surface imparta lesser gripping action which gradually increases toward the smallerdiameter of said surface.

3. A strand chuck for the purpose described comprising a body having afrusto-conical bore of some predetermined angle of taper and a pluralityof generally wedgeshaped jaws operating as a set jointly movable axiallyin said bore into converging relation, said jaws each having an arcuateexterior surface for abutting engagement with the wall of the bore andan interior surface gripping the strand upon convergence of the jaws,said interior surfaces, when in gripping relation with the strand, lyingon a common, substantially cylindrical surface, the exterior slantsurface of a longitudinal portion of each jaw extending inwardly fromthe smaller end of the jaw a distance of substantially one-third toone-half of the axially-measured length of the jaw having a taper, measured when the jaws are not converged into said gripping relation, whichis of some angle greater than the taper of the bore, the remainder ofsaid exterior jaw surface measured in the same manner, having the sametaper as the bore, all tapers being referred as acute angles to thecommon longitudinal axis of the bore and jaws whereby, when the jaws arefully converged, the said exterior jaw portions are deformed radiallyoutwardly into abutting relation with the wall of the bore.

4. A strand chuck for the purpose described comprising a body having afrusto-conical bore of some predetermined angle of taper and a pluralityof generally wedge-shaped jaws operating as a set jointly movableaxially in said bore into converging relation, said jaws each having anarcuate exterior surface for abutting engagement with the wall of thebore and an interior surface gripping the strand upon convergence of thejaws, said interior surfaces, when in gripping relation with the strand,lying on a common, substantially cylindrical surface, the exterior slantsurface of a longitudinal portion of each jaw extending inwardly fromthe smaller end of the jaw a distance of at least one-half of theaxiallymeasured length of the jaw having a taper, measured when the jawsare not converged into said gripping relation, which is of some anglegreater than the taper of the bore, the remainder of said exterior jawsurface measured in the same manner, having the same taper as the bore,all tapers being referred as acute angles to the common longitudinalaxis of the bore and jaws. whereby, when the jaws are fully converged,the said exterior jaw portions are deformed radially outwardly intoabutting relation with the wall of the bore.

5. A strand chuck for the purpose described comprising a body having afrusto-conical bore of some predetermined angle of taper and a pluralityof generally wedge-shaped jaws operating as a set jointly movableaxially in said bore into converging relation, saidjaws each having anarcuateexterior surface for abutting engagement with the wall of thebore and an interior surface gripping the strand upon convergence of thejaws, said; interior surfaces, when in gripping relation withthe strand,lying on a common, substantially cylindrical surface, the entire slant,exterior surface of each jaw having a taper which is of some anglegreater than the taper, measured when the jaws are not converged intosaid gripping relation of the bore, both tapers being referred as acuteangles to the common longitudinal axis of the bore and jaws whereby,when the jaws are fully said slant. surfaces in abutting relation. withthe wall of the bore. 7

References Cited by the Examiner UNITED STATES PATENTS M. HENSON WOOD,In, Primary Examiner.

converged, the same are urged radially outwardly with 5 DONLEY STOCKING,Examinell UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo 3,1o3 ,904 January 5, i965 Ronald P. Ziolkowski It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 7, line 10, after "taper" insert measured when the jaws are notconverged into said gripping relation, same column 7, lines 11 and 12,strike out measured when the jaws are not converged into said grippingrelation Signed and sealed this 18th day of May 1965* (SEAL) Attest:

ERNEST w. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent V03,163 ,o-O l 7 January 5, 1965 Ronald P. Ziolkowski It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 7, line 10, after "taper" insert H measured when the jaws are notconverged into said gripping relation, same column 7, lines 11 and 12,strike out measured when the jaws are not converged into said grippingrelation Signed and sealed this 18th day of May 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Aitesting Officer Commissioner ofPatents

3. A STRAND CHUCK FOR THE PURPOSE DESCRIBED COMPRISING A BODY HAVING AFRUSTO-CONICAL BORE OF SOME PREDETERMINED ANGLE OF TAPER AND A PLURALITYOF GENERALLY WEDGESHAPED JAWS OPERATING AS A SET JOINTLY MOVABLE AXIALLYIN SAID BORE INTO CONVERGING RELATION, SAID JAWS EACH HAVING AN ARCUATEEXTERIOR SURFACE FOR ABUTTING ENGAGEMENT WITH THE WALL OF THE BORE ANDAN INTERIOR SURFACE GRIPPING THE STRAND UPON CONVERGENCE OF THE JAWS,SAID INTERIOR SURFACES, WHEN IN GRIPPING RELATION WITH THE STRAND, LYINGON A COMMON, SUBSTANTIALLY CYLINDRICAL SURFACE, THE EXTERIOR SLANTSURFACE OF A LONGITUDINAL PORTION OF EACH JAW EXTENDING INWARDLY FROMTHE SMALLER END OF THE JAW A DISTANCE OF SUBSTANTIALLY ONE-THIRD TOONE-HALF OF THE AXIALLY-MEASURED LENGTH OF THE JAW HAVING A TAPER,MEASSURED WHEN THE JAWS ARE NOT CONVERGED INTO SAID GRIPPING RELATION,WHICH IS OF SOME ANGLE GREATER THAN THE TAPER OF THE BORE, THE REMAINDEROF SAID EXTERIOR JAW SURFACE MEASURED IN THE SAME MANNER, HAVING THESAME TAPER AS THE BORE, ALL TAPERS BEING REFERRED AS ACUTE ANGLES TO THECOMMON LONGITUDINAL AXIS OF THE BORE AND JAWS WHEREBY, WHEN THE JAWS AREFULLY CONVERGED, THE SAID EXTERIOR JAW PORTIONS ARE DEFORMED RADIALLYOUTWARDLY INTO ABUTTING RELATION WITH THE WALL OF THE BORE.